CVS is a powerful method of allowing many developers to work on the same source code. This is possible because each developer checks out a copy of the current version of the source code. Then they each independently work on their personal copy of the sources. When they have made changes, they commit them back to the CVS repository. The CVS server takes care of things like trying to merge their changes with those of others. When that doesn't work, the developer is notified and they do a hand merge of the conflicts.
To try out the latest versions of the code, you don't have to usually worry about all that. You will just need to understand how to check out packages. Understand, however, that you are looking at the very latest version - it might not even build, or it might core dump instantly. That is ok, as the people working on it will fix those problems before a stable release is made. So don't email them about the problems you find!
First you need to setup a few environmental variables.
The first command you need is:
$ export CVSROOT=':pserver:firstname.lastname@example.org:/cvsroot/gastro'
You might want to put this in your login script.
Then do the command:
$ cvs login
When prompted for a password for anonymous, simply press the Enter key. This only needs to be done only ONCE, not everytime you access CVS.
Now grab the package you need. The first time you will want to do something like:
$ cvs -z3 checkout Gastropod
Please use the -z3 option to minimize network bandwidth (-z9 eats too much CPU time - please don't use it).
Now you will want to go through and build and install the packages (see installation notes and the INSTALL file).
After you have checked the code out, you can use:
$ cvs -z3 update -Pd Gastropod
Familiarise yourself with the cvs documentation.
Here is a CVS FAQ of sorts.